Process for producing xylose

ABSTRACT

Material containing cellulose, lignins and xylan is hydrolyzed and the resulting aqueous solution is extracted with methanol to obtain crystalline xylose. The xylose may be hydrogenated to produce xylitol.

United States Patent 1191 Jaffe et al. Jan. 8, 1974 1 PROCESS FORPRODUCING XYLOSE 3,579,380 5/1971 Fll6S6 260/635 c 1 2,944,922 7 1960 B0127 37 [75] Inventors: Gerald Myer Jaffe;W1ll|am 2,959,500 $1960 filslkrybaloi both of Verona; Peter 2,974,067 3/1961 Apel 127 37 Hans W inrt, ay a of Ni 2,989,569 6/1961 Apel 127 37 x 3,212,932 10/1965 Hess 12737 [73] Assgnee gg Nufley1 3,479,248 10/1969 NOblle 127/37 x OTHERPUBLICATIONS 22 F' d: 1 1 1 9 Wolfrom et al., J.A.C.S., v61. 64, page1739, 1942. PP N98 72,898 Hudson 6t 3]., JACS, v61. 40, pages 1601-1602,1918.

Related US. Application Data P [63] Continuation-in-part of Ser. No863,358, Oct. 29, nrfmry Exam".1er M.0rns Wonk 1969 abandone AsszstantExammer--S1dney Marantz Attorney-Samuel L. Welt, Jon S. Saxe, Bernard S.521 [1.5. Ci. 127/37, 260/124 R, 260/635 c L60, William R Epstein andGemge [51] Int. Cl Cl3k 9/00 [58] Field 61 Search 260/602, 635 c; [571ABSTRACT 127/37 Material containing cellulose, lignins and xylan ishydrolyzed and the resulting aqueous solution is ex- [56] ReferencesCited tracted with methanol to obtain crystalline xylose. The

UNITED STATES PATENTS xylose may be hydrogenated to produce xylitol.3,558,725 111971 14611116 et al. 260/635 0 5 Claims, No Drawings CROSSREFERENCE To RELATED APPLICATIONS This application is acontinuation-impart of United States Patent Application Ser. No. 863,358filed Oct. 29, 1969 now abandoned.

BACKGROUND OF THE INVENTION separated into the individual componentswith great difficulty and high losses. Furthermore, these separa tionand purification techniques have proven to be both expensive andtime-consuming;

The xylose which is produced by these processes in order to be utilizedas an intermediate for xylitol must be subjected to reduction. Thereduction of the aldehyde or keto groups of reducingsugars such asxylose to produce xylitol has been carried out by known methods such asin a chemical or catalytic manner. For example, xylose has been reducedto xylitol with the aid of a sodium amalgam or in the presence of anickel catalyst. However, in order to carryout this reaction, it isnecessary to utilize pure xylose since slight impurities, particularlylignins, can poison the catalyst and cause a standstill in thisreduction step. This standstill results in not being able to resume thereduction reaction.

In order to overcome these disadvantages, it has been proposed toproduce xylose by utilizing as starting materials only those materialswhich have a high xylose content and a low lignin content. Thesematerials are rather expensive and impurities still have to be removedfrom the xylose by expensive and timeconsurning procedures with highlosses. Therefore, it has long been desired to provide a means forproducing substantially chemically pure xylose from inexpensivecellulose materials without the necessity for utilizing cumbersomeseparation procedures.

SUMMARY OF THE INVENTION In accordance with this invention,substantially chemically pure xylose for direct conversion into xylitolcan be produced from cellulose and xylan containin g materials by firsttreating these extracts with an acid hydrolyzing agent in an aqueousmedium to precipitate the lignins. The resulting aqueous solution isthen passed through an ion exchange resin bed and the effluent from saidbed which is dried is dissolved in methanol forming xylose as acrystalline material. The crystalline xylose which is isolated from themethanolic solution can be dissolved in an aqueous medium andhydrogenated in the conventional manner to form xylitol.

In accordance with this process, it has been found that the xyloseproduced has such a high degree of purity that hydrogenation of thexylose proceeds without the danger of the hydrogenation coming to astandstill. Furthermore, by this process, substantially chemically purexylose can be obtained from aqueous hemicellulose extracts such as woodextracts which are waste material of the paper and wood industry withoutthe necessity for utilizing expensive-and cumbersome separation andpurification techniques.

DETAILED DESCRIPTION In accordance with this invention, xylitol isproduced by hydrogenating xylose which has been isolated from aqueousextracts of hemicellulose materials.

In accordance with this invention, xylitol is produced by hydrogenatingxylose which has been produced from hemi-cellulosic materials. As thestarting material, any cellulosic material containing xylan andcellulose can be utilized. These cellulosic materials generally containlignins and carbohydrates which are mix tures of monomers and polymersof saccharide materials such as hexoses and pentoses. The cellulosicmaterials which can be utilized can be in the form of a dried groundmaterial or in the form of an aqueous extract of a hemicellulosicmaterial. Among the suitable cellulosic materials for carrying out theprocess in accordance with this invention are included all angiosperms,that is both monocotyledonous plants such as grasses (e.g., oats,bagasse or maize) and dicotyledonous plants such as conifers, decidoustrees (e.g., beech, poplar, birch or alder). Of the starting materialsquoted by way of example, beechwood, which is available in largequantities and has small economic value, is especially useful.Especially suitable are freshly cut and air-dried beechwood shavings,oat hulls and corn cobs.

If it is desired to utilize extracts in the process of this invention,these extracts can be'obtained by treating hemi-cellulose materials withwater or steam at temper atures of from 110C. to I" C. and at pressuresof from about l5 to 20 pounds per square inch gauge. The steam or waterextracts the carbohydrates and lignins from the cellulose materialsintoan aqueous medium. These extracts generally contain lignins,polysaccharides and monosaccharides. The monosaccharides include pentoseand hexose sugars such as glucose, mannose, galactose, xylose andarabinose. The polysaccharides include the polymeric forms of thesehexose and pentose sugars. Generally, based upon its solids content,aqueous extracts of hemicellulose materials such as aqueous woodextracts contain from an 5 to 30 percent bp weight of lignins and from70 to percent by weight of carbohydrates which include bothpolysaccharides and monosaccharides. These aqueous hemicelluloseextracts usually contain from l0 to-40 percent by weight of xylose,based upon the solids content of the extract.

These aqueous hemicellulose extracts are generally prepared as anaqueous solution or in the form of a concentrated liquid, i.e., a liquidhaving a solids content of from 40 to 60 percent and a water content offrom 40 to 60 percent by weight. The amount of constituents andcomponents in the solids of the wood extracts vary according to theseason of the year, the type of wood, and the wood treating conditions.By way of example, hard wood provides a higher amount of pentose sugarsthan soft wood and, in this connection, the carbohydrates in the woodhydrolysates are predominantly pentoses. On the other hand,in the caseof the treatment of soft wood, carbohydrates in the extracts are mainlyhexoses. The use of these extracts is desirable since they are regardedas waste products of the pulp and paper industry.

In the first step of this process, an aqueous solution containing thecellulosic material is hydrolyzed with an acid hydrolyzing agent. Anyconventional acid hydrolyzing agent can be utilized such as theinorganic mineral acids, i.e., sulfuric acid, hydrochloric acid, etc.and the organic acids such as halogenated lower alkanoic acids, i.e.,trichloroacetic acid,'monochloroacetic acid, etc. Generally, inorganicacids such as sulfuric acid are preferred in this process. The inorganicacids can be utilized in either their dilute or concentrated forms. Theacid hydrolyzing agent can be present in the aqueous solution in anamount of from about 1 percent by weight to about 20 percent by weightof the cellulosic material to be hydrolyzed. The treatment with the acidhydrolyzes the polysaccharides to the monosaccharides and converts thelignins into insoluble material which can be removed by filtration.These hydrolysis reactions can take place at room temperature, i.e.,about 20C. Generally, it is preferred, in carrying out these hydrolysisreactions to utilize elevated temperatures, i.e., from 55C. to 150C.Atmospheric pressure or elevated pressure can be utilized. Generally, itis preferred to carry out this hydrolysis under pressure, i.e., fromabout 5 to 100 p.s.i.g.

This hydrolysis reaction converts the polysaccharides in the cellulosicmaterials to monosaccharides and the lignins to insoluble lignins. Theseinsoluble lignins precipitate from the aqueous solution upon hydrolysis.These insoluble lignins can be removed from the aqueous solutioncontaining the mixture of monosaccharides by conventional means such asfiltration.

After filtration, the aqueous solution is passed through an ion exchangeresin bed. Any conventional cationic or anionic ion exchange resin canbe utilized for the purposes of the present invention.

The anionic ion exchange resins employed for the purposes of the presentinvention include, e.g., crosslinked polystyrene containing quaternaryammonium groups or substituted amines such as -N(C H groups,polycondensation products of phenol and formaldehyde containing aminogroups, polymerization products of aromatic amines and formaldehyde,guanidine-formaldehyde resins, polyamines, phenolformaldehyde resins,etc. These anionic resins are commercially available under such tradenames as:

Amberlite (types lR-4B, lR-45, IRA-410, IRA-93,

IRA-400) (Rohm & Haas) Dowex (types 1 and 2) Dow Corning) Wofatite M (l.G. Farben) Permutit S (Permutit A.G.)

Kastel A-300 etc. (Montecatini) Permutit D.R. (Permutit A.G.)

Any conventional cationic ion exchange resin can be utilized in thisreaction. Among the preferred cationic ion exchange resins are includedthe nuclear sulfonic acid cationic ion exchange resins such aspolystyrene sulfonic acid type resins sold under trade names such aslR-120 and Dowex 50.

In accordance with a preferred embodiment of this invention, the aqueoussolution is passed first through a cationic ion exchange resin bed andthen through an anionic ion exchange resin bed. However, in accordancewith this invention, the aqueous solution can be passed either through acationic ion exchange resin bed or through an anionic ion exchange resinbed.

In accordance with this invention, it has been found that filtration ofthe aqueous solution through the ion exchange resin bed decolorizes theaqueous solution and removes any entrained lignin particles. Theeffluent coming from the column is decolorized and has all of the ligninparticles removed therefrom.

In accordance with the process of this invention, the effluent from theion exchange resin treatment, in the next step, is dried to a watercontent of from 5 to 15 percent by weight. Any conventional means ofdrying the effluent can be utilized in accordance with this invention.These methods include evaporation, roll or spray drying. The evaporationcan take place by use of high temperature or vacuum conditions. Thedried product can be either a powder containing about 5 percent byweight of water or a viscous syrup containing about 15 percent by weightof water.

After the effluent from the ion exchange resin treatment has been driedto a water content of from 5 to 15 percent, the dried effluent isdissolved in methanol. The pH of the effluent which is dissolved in themethanol should be from 4 to 8. If necessary, the pH of the effluent canbe adjusted within this range by the addition of a small amount of analkali or alkaline earth metal hydroxide or an alkali metal or alkalineearth metal salt. Among the additives which can be utilized to adjustthe pH of the effluent are included sodium hydroxide, potassiumhydroxide, calcium hydroxide, magnesium hydroxide, sodium bicarbonate,sodium phosphate, calcium carbonate, etc. The adjustment of the pH ofthe effluent to a value of from 4 to 8 can take place prior to dryingthe effluent. On the other hand, the pH of the effluent can be adjustedafter drying has taken place.

The dried effluent is mixed with the methanol so that the effluentdissolves in the methanol. The amount of methanol needed should besufficient to dissolve the effluent. Generally, it is preferred toutilize at least 0.5 ml. of methanol per gram of the dried effluent.Large excesses of methanol, i.e., ml. of methanol per gram of effluentcan be utilized, if desired. However, since no beneficial results areachieved by utilizing such large excesses, i.e., amounts of greater than100 ml. of methanol per gram of dried effluent, these large amounts areseldom utilized. I

The dried effluent can be mixed with the methanol by any conventionalprocedure. In carrying out this mixing step, temperature and pressureare not critical, and this mixing step can be carried out at roomtemperature. However, if desired, elevated or reduced temperatures canbe utilized. Generally, it is preferred to carry out this mixing step ata temperature offrom 10 to 50C.

In accordance with this invention, it has been found that methanol willdissolve all of the materials in the hydrolyzed cellulosic materialsthat have been passed through an ionic exchange resin bed except for thexylose contained therein. Hence, by dissolving the hydrolyzed cellulosicmaterials in methanol, the xylose is crystallized in substantially pureform from the solution. Furthermore, by a means of the process of thisinvention, the xylose which is obtained as a crystalline precipitate isseparated from all of the impurities and other constituents originallypresent in the cellulosic material. Therefore, the process of thisinvention produces xylose in substantially chemically pure form.

The xylose can be separated from the methanolic solution by anyconventional means such as filtration.

After separation in crystalline form, the xylose can be converted toxylitol.

The xylose which is isolated in crystalline form from the methanolicsolution can be converted to xylitol by utilizing any conventional meansfor converting an aldehyde or keto group to an alcohol. Generally,xylose is converted to the xylitol by hydrogenation in an aqueousmedium. This hydrogenation can be carried out in a chemical or catalyticway, for example, with sodium amalgam or a complex metal hydride such aslithium borohyd'ride or sodium borohydride. Preferably a noble-metalcatalyst such as platinum or palladium is utilized. Especially preferredare'nickel catalysts such as Raney-nickel. However, any conventionalmeans of hydrogenating an aldehyde or ketone can be utilized inaccordance with this invention.

The hydrogenation can be carried out under any conventionalhydrogenating conditions. Any temperature of from about 70C. to 120C.and hydrogen pressures of from about atm. (gauge) to about 50 atm.(gauge) can be utilized. The hydrogenation of xylose to xylitol ispreferably carried outin an aqueous medium at a pH of 3 to 10,preferably from 6 to 8 and at a hydrogen atmosphere of about 30 atm.(gauge) and at a temperature of 105 to 1 10C. The hydrogenation proceedsquantitatively. The solid catalyst system can be easily removed from thehydrogenated aqueous solution containing the xylitol by conventionalprocesses such as filtration.

1n accordance with this invention the hydrogenated reaction solutioncontaining the xylitol can, if desired, be passed through a cationic ionexchange resin bed. Any conventional cationic ion exchange resins suchas those mentioned hereinbefore can be utilized. After passing thereaction medium containing the xylitol through the cationic ion exchangeresin bed, the reaction medium can be passed, if desired, through ananionic ion exchange resin bed; Any conventional anionic ion exchangeresin, such as those mentioned hereinbefore, can be utilized inaccordance with this invention. 4

By successively passing the hydrogenated reaction medium through acationic ion exchange resin bed and then through an anionic ion exchangeresin bed, all entrained and residual impurities are removed from thexylitol. The effluent from these beds is colorless liquid. The xylitolcan be recovered from the effluent by conventional means such asevaporation.

The invention is further illustrated by the following examples, whichare illustrative but not limitative of the claimed invention.

EXAMPLE 1 To 517 ml. water, there was added 100 g. of Masonex syrup, anaqueous wood extract having the following composition: 1

After the Masonex was mixed with water, 4.4 ml. of concentrated sulfuricacid was added, giving a total volume of 600 ml. of dark brown solution.100 ml. of this solution containing 16.7 g. Masonex was heated in asealed 200 ml. heavy-walled Pyrex pressure flask at 120C. for 6 hours.The black-brown hydrolyzate was cooled, filtered, and washed with atotal of ml. water. It contained 2.63 g. xylose. The filtrate was passedthrough 120 ml. Amberlite 1R-120 resin (H cycle) followed by passagethrough 120 ml. Amberlite IRA-93 resin (Ol-l' cycle). Each resin columnwas washed with 500 ml. water.

EXAMPLE 2 Isolation of Xylose The combined eluents and washes preparedin Example l were evaporated under vacuum (45C. bath) and 7.2 g. of asyrup containing 1 g. of water was obtained.

This syrup was dissolved in 7.0 'ml. of methanol. Xylose EXAMPLE 3Preparation of Xylitol 10.28 g. of xylose which were prepared in Example2, were dissolved in 22 ml. of water (deionized). The solution was mixedwith 2.0 g. of Haney-nickel (50 percent aqueous suspension) and 0.3 g.of calcium carbonate. The mixture was hydrogenated at C. i 5 and 450p.s.i.g. for 4.5 hours. The reaction was cooled to room temperature,filtered and the solids washed with water.

The clear colorless filtrate was deionized by successive passage firstthrough a column of 20 ml. of Amberlite IR [polystyrene divinyl benzenesulfonate cation ion exchange resin in its H form] and then through acolumn of 20 ml. of Amberlite IRA 93 [polystyrene divinyl benzenetertiary amine anion exchange resin in its OH form]. The column waswashed twice, each time with 50 ml. of water (deionized). The combinedeluants were concentrated under vacuum at 4045C. to a syrup (11.2 g).Then 12.0 ml. of methanol were added and the viscous solution wasstirred at 25C. until crystallization started. The stirring wascontinued and the suspension was stirred at 0-3C. overnight. The mixturewas filtered to separate the solids from the mother liquor. The solidsobtained by filtration were washed three times with a total of 50 ml. ofmethanol (cooled to -l0C.). The solids were dried at 35C. under vacuum.The wash mother liquors were concentrated under vacuumito 1,5 g. ofresidue which was dissolved in 2.0 ml. of methanol and refrigerated(0-3C.) overnight. The second crop was isolated from the filtered motherliquor by crystallization with methanol as described above.

Xylitol Recovery Yield 9.0 g. or 92.1% based on Xylose.

EXAMPLE 4 Preparation of Xylose from Oat Hulls To 480.0 g. water therewere added 59 ml. concentrated hydrochloric acid (37 percent by weightHCl) and 120.0 g. of dried, ground oat hulls having the followingcomposition:

1. Water 7.8 percent 2. Solids 92.2 percent a. Ash 5.4 percent b.Carbohydrates present in their polysaccharide form. l. Arabinose 2.2percent 2. Xylose 21.5 percent 3. Galactose 0.7 percent 4. Glucose 2.4percent 5. Mannose trace 6. Other hemicelluloses and proteins 8-10percent The suspension was hydrolyzed for three hours at l l8C.l20C. Thehydrolysis mixture was cooled, centrifuged, and the solids were washedwith 400 cc. of water. The clear, yellow filtrate containing 25.8 g.xylose was deionized by passing it successively through two ion exchangeresin columns, the firstone containing 70 ml. Amberlite 1R-120 resin (Hform) and the second one containing 170 ml. Amberlite IRA-93 resin (OH),at 7 m1./minute. Each resin column was washed with two column volumes ofwater. The eluent and washes were combined and concentrated at .4044C.under vacuum to asyrup weighing 42.8 g.

and containing about 4.1 g. of water. To the syrup was added 43.9 ml.methanol. The yellow solution was cooled to 10C. and agitated at thattemperature for 48 hours. Crystallization of xylose took place duringthat time. The crystalline suspension was filtered, washed with 4 X 10ml. methanol at -10C., and dried to a constant weight of 18.0 g. xylosewith a purity of 94.0 percent. The chemical yield of xylose based on oathulls is therefore 14 percent.

EXAMPLE 5 Hydrogenation of Xylose to Xylitol 15.0 g. of xylose preparedin Example 4 were dissolved in 22.5 ml. of water and filtered. Theclear, light yellow filtrate was deionized by passing it through a 10liter Amberlite 1R-120 resin column (H followed by passage through a 10ml. Amberlite lRA-93 resin column at 2 ml./minute. Each resin column waswashed with 20 ml. water.

The combined eluent and washes were mixed with 3.0 g. Raney Nickelcatalyst (50 percent by weight aqueous suspension) and 0.015 g. calciumcarbonate. The mixture was hydrogenated at 100C. at 450 p.s.i.g. H for1.5 hours. The mixture was cooled to 25C. and filtered. The clear,colorless filtrate was passed through a 4 ml. Amberlite lR-l20 resincolumn (H*) and concentrated at 45C. under vacuum to a thick syrupcontaining 91.2 percent solids. 15 ml. of a mixture containing percentby volume of ethanol and 70 percent by volume of methanol were added andthe total mixture was cooled to 0C. Crystallization of xylitol tookplace during this period. The crystalline suspension was agitated at 0C.for 48 hours, filtered, washed with 8 ml. of 95 percent by volumeethanol and 5 percent by volume water followed by 2 X 5 ml. of ethanol,and dried to constant weight of 12.2 g. The purity of the isolatedxylitol is 99+ percent by glpc. It melts at 93-95C. The yield of xylitolfrom oat hulls thus is 12.1 percent.

We claim: I

l. A process for producing xylose from a cellulosic material containingcellulose, lignins, xylan and other carbohydrates, which comprises thesteps of a. hydrolyzing said cellulosic material with an acid in anaqueous medium to produce an insoluble lignin residue;

b. separating said insoluble lignin residue from the hydrolyzed aqueousmedium;

0. passing the hydrolyzed aqueous medium through an ion exchange resinbed;

d. drying the effluent from said bed to a water content of from about 5to 15 percent by weight, the pH of said effluent being adjusted to about4 to 8; and

e. mixing said dried effluent in methanol to form a methanolic solution,and crystallizing xylose as a crystalline precipitate from saidmethanolic solutlon.

2. The process of claim 1 wherein said material is aqueous cellulosicextracts.

3. The process of claim 1 wherein said material is dried ground oathulls.

4. The process of claim 1 wherein the methanol in step (e) is added inan amount of at least 0.5 ml. per gram of the dried effluent.

5. The process of claim 1 wherein said extracts are aqueous extractionproducts of hard wood.

2. The process of claim 1 wherein said material is aqueous cellulosicextracts.
 3. The process of claim 1 wherein said material is driedground oat hulls.
 4. The process of claim 1 wherein the methanol in step(e) is added in an amount of at least 0.5 ml. per gram of the driedeffluent.
 5. The process of claim 1 wherein said extracts are aqueousextraction products of hard wood.